A conventional thin film micromechanical resonator gyro is disclosed in, for example, U.S. Pat. No. 5,438,231.
The resonator gyro is described referring to FIG. 14 and FIG. 15.
FIG. 14 shows a perspective view of the resonator gyro.
FIG. 15 shows a cross sectional view of the resonator gyro at the drive section, sectioned along the line 15—15 of FIG. 14.
Referring to FIG. 14, tuning fork 101 has two arms 102, 103 made of non-piezoelectric material. Piezoelectric thin films 104 and 105 are disposed on the main surface of respective arms 102 and 103 of tuning fork 101. Electrodes 106, 107, 108, 109, 110 and 111 are coupled with respective piezoelectric thin films 104, 105. Application of an alternating voltage to electrodes 107, 108, 110 and 111 causes tuning fork 101 to resonate.
In FIG. 15, a space of width 131 is shown on piezoelectric thin film 104 with respect to center line 121 of arm 102, where there is no electrodes 107, 108 provided above. Arrow mark 141 indicates the direction of electric field working to piezoelectric thin film 104 from electrode 107 to electrode 108.
In the above-described thin film micromechanical resonator gyro, electrode 106 opposing to respective electrodes 107 and 108 has a continuous sheet form. As a result, a component of electric field as indicated by arrow mark 141 readily arises. The component is irrelevant to the driving of resonator gyro.
Piezoelectric thin film 104 disposed beneath electrodes 107 and 108 also has a continuous sheet form. As a result, when piezo film 104 at the portion sandwiched by electrode 107 and electrode 106 tries to stretch in the Y axis direction, for example, piezo film 104 corresponding to the portion of width 131 retards the stretching try. In the same manner, when piezo film 104 at the portion sandwiched by electrode 108 and electrode 106 tries to shrink in the Y axis direction, the portion of width 131 retards the shrinking try.
The drive efficiency of tuning fork 101 is sometimes deteriorated by the above described factors.